Copolymers of dimethyl itaconate and conjugated diolefins



Patented Nov. 25, 1952 UNITED STATES PTENT OFFICE COPOLYMERS OF DIMETHYL ITACONATE AND CONJUGATED DIOLEFINS No Drawing. Application May 7, 1949, Serial No. 92,088

This invention relates to polymers of olefin polycarboxylic acid esters. More particularly, it relates to resinous copolymers of a major proportion of dimethyl itaconate and a minor proportion of butadiene or the like.

The copolymerization of various vinyl esters such as methyl acrylate or tri-butyl aconitate with diolefin hydrocarbons has been suggested previously in connection with the preparation of soft rubbery synthetic polymers. However, it has now been discovered that dimethyl itaconate behaves in an unexpected manner as compared with previously used vinyl esters and that by proper selection of the monomer ratio of dimethyl itaconate to diolefin, leather-like thermoplastic resins can be obtained which posses unusual oil resistance and excellent processing properties.

According to this invention resinous products are obtained by copolymerizing in aqueous emulsion about 65 to 90 parts by Weight of dimethyl itaconate and about 35 to 10 parts by weight of a conjugated C4 to C6 diolefin such as butadiene-1,3, isoprene or dimethyl butadiene. Within the stated range copolymers prepared from 75 to 80 parts of dimethyl itaconate and to 20 parts of butadiene-l,3 are particularly preferred. Minor amounts, e. g. 10 to parts of the dimethyl itaconate may be replaced in the polymerization mixture by a third monomer such as styrene, methyl methacrylate, vinyl pyridine, isobutylene and the like. I V I The polymerization reaction is carried out by emulsifying the reaction monomers in an aqueous medium, the weight ratio of monomers to water being-from about 2:1 to 1:10, ratios between 1:2 and 1:4 being usually preferred. Any commonly known emulsifying agent may be used herein in the usual manner. For example, about 0.5 to 8% by weight of monomers of an ammonium or an alkali metal soap of a saturated or unsaturated C8 to C24 fatty acid such as caprylic, carnaubic, lauric or mixed coconut oil acid can be used, but the sodium or potassium salts of oleic or stearic acids are preferred. In addition to or in place of the fatty acid soap, another emulsifier such as Daxad-ll (sodium salt of 9. formaldehyde condensation product of naphthalene sulfonic acids) or sodium lauryl sulfate, sodium tetraiscbutylene sulfonate, for aromatic alkyl sulfonate salts, etc. may be used to advantage.

The polymerization may be carried out at temperatures ranging from about 20 C. to +60 C., temperatures between 30 C. and 50 C. be-

13 Claims. (Cl. 260-323) ing preferred. Polymerizations at temperatures between -20 C. and +20 C. are hereafter referred to as low temperature polymerizations. When the polymerization temperature is below the natural freezing temperature of the aqueous emulsion, it is necessary to add to the emulsion a suflicient amount of an anti-freeze agent to prevent the reaction mixture from freezing. Suitable anti-freeze agents are saturated monoor polyhydric aliphatic alcohols of 1 to 3 carbon atoms, such as methanol, ethanol, ethylene glycol, propylene glycol, or glycerol. Ordinarily the polymerization times may vary between about 5 and 48 hours depending on temperature, degree of conversion desired, catalyst system and other known variables in the polymerization procedure, times of about 10 to 15 hours being ordinarily preferred. The total reaction may be carried to a conversion of about 50 to 100%, preferably to The catalyst used may be any one or a mixture of the known class of per-type or oxygen-liberat ing catalysts used in emulsion polymerizations such as hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide, potassium persulfate or other alkali persulfates or perborates or the corresponding ammonium salts. The oxygen-liberating catalyst is used in amounts ranging from about 0.03 to 2% based on the weight of monomers, catalyst concentration ranging from 0.3 to 0.5% of potassium or other alkali persulfate being preferred for polymerizations carried out above room temperature while concentrations of about 0.05 to 0.3% of the more reactive organic peroxides such as cumene hydroperoxide are preferred in low temperature polymerizations.

Furthermore, a total of 0.1-1.0 part (based on 100 parts of monomers charged) of a primary or tertiary aliphatic mercaptan having at least 6 and up to about 18 carbon atoms, e. g. hexyl, dodecyl, tetradecyl or octadecyl mercaptan, or mixtures of C6 to C18 mercaptans, or other modifiers such as diisopropyl dixanthogen disulfide, are likewise beneficially present in the reaction mixture to promote the polymerization and to obtain polymers of predetermined plasticity. All of the modifier may be added to the emulsion at the beginning, but it is preferred toadd only about 0.1 to 0.8 part to the initial charge and to introduce further amounts later, e. g. add another 0.1 to 0.5part when total conversion has reached about 40 to "70%. As an alternative, the modifier may also be added continuously.

Other factors whereby the molecular weight of the product, reaction rate, or both, may be effected are polymerization temperature, monomer ratio, conversion, etc., as is well known per se. Furthermore, activation of the polymerization reaction may be accomplished by carrying out the polymerization in the presence of potassium ferricyanide, hydrocyanic acid or morpholine or in a so-called redox system such as is described, for example, in Industrial and Engineering Chemistry, vol. 40, pp. 770, 772, 773- 777 and 932-937 (1948).

The invention is more fully illustrated by the following examples in which the term parts refers to parts by weight.

EXAMPLE 1 The following charge was emulsified in a pressure container and polymerized at 45 C. for 16 hours:

25 parts butadiene-l,3

75 parts dimethyl itaconate 180 parts water 4 parts sodium oleate 0.3 part potassium persulfate 0.4 part lauryl mercaptan The resulting latex was short-stopped with 0.1 part of hydroquinone on monomers and coagulated with an aqueous solution of sodium chloride. The coagulated polymer was washed on a mill to free it of soap and other impurities and the washed polymer was mill-dried at 70 C. A transparent, colorless, flexible, thermoplastic, smooth sheet of polymer was obtained in a yield indicating 100% conversion of monomers to polymer. By analysis the product contained about 72 weight percent of combined dimethyl itaconate. Thin films having a tensile strength of 800 lbs/sq. in. and higher were readily obtained from the raw polymer by calendering. The polymer was highly resistant to a variety of organic solvents as shown in Table I.

Solutions of the novel polymers in appropriate solvents, in concentrations of about to are useful as coating compositions. For example, when a 15% solution of this polymer in methylethyl ketone was cast on polished steel panels and air-dried, protective film-s characterized by excellent oil and grease resistance, good hardness and flexibility, fair adhesion and caustic reslstance, but of relatively poor resistance to soap and water were obtained. Coatings prepared by baking the cast films in an oven at 80 C. for 15 minutes had similar properties as those just mentioned except that the soap resistance of the baked film was materially improved. Baking of the novel unvulcanized resins at temperatures between 60 and 110 C. for periods ranging from 5 minutes to 1 hour is generally helpful. Furthermore, it was found possible to get excellent adhesion of the dried film by adding about 5.0 parts of ethylene glycol or glycerol and a trace of acid catalyst such as toluene sulfcnic acid,

EXAMPLE 2 Other copolymers were prepared by polymerizing the following charges at 50 C. for 15 hours:

Run No Butadiene-l, 3, Parts Dimethyl itaconate, 1 Parts" Sodium lauryl sulfate, Parts Water, Parts Mercaptan Modifier, Parts Potassium Pei-sulfate, Parts Conversion, percent 1 Ovrus Paste.

2 Lorol Mercaptan (a mixture of Ca to Cl! primary mermptsns containing a major proportion of lauryl mercaptan).

The polymeric products were recovered from the resulting latex and finished in the conventional manner described in Example 1. The polymers, compounded with 0.5 weight percent of 2,6-di-t-buty1-4-methyl phenol, were clear, tough, leathery, gave a smooth rolling bank on the mill and were taken off the mill as a smooth sheet similar in all respects to the product described in Example 1. By analysis product A contained about and product B contained about 76% of combined dimethyl itaconate.

Sheets of these raw polymers pressed at 141 C. for 15 minutes had a tensile strength of 750 to 900 lbs. per sq. in. and an ultimate elongation of 150 to 250% (determined on test pads 6" x 6 x 0.075).

When polymer A was compounded for vulcanization and cured for ten minutes at 141 C. in a steam heated press, tensile values could not be determined since the cured stock was hormr and too brittle to pull. By contrast, when polymer B was similarly compounded and cured, a strong, leather-like and flexible vulcanizate having the following properties was obtained:

. Tensile, Elongation Cum Tune (Mm') p. s. 1. Percent Parts Polymer Stearic acid 1 Zinc oxide 5 Sulfur 1 Tetramethyl thiuram disulfide 1 EXAMPLE 3 When Example 2 was repeated using a butadiene/itaconate monomer ratio of 40/60, a soft, rough, rubber-like product was obtained which had much poorer oil resistance than the polymers described above. The rubber-like product was very diflicult to mill, possessed only a slight amount of thermoplastic behavior, and gave rough gnarled sheets. When compounded and cured according to the procedure stated in Example 2, an elastic vulcanizate having the f llowing properties was obtained:

This example illustrates that copolymers of less than, 65 percent dimethyl itaccnate do not yield the tough resins desired in accordance with this invention, but instead lead to soft elastic products whose tensile strength is equal to only a fraction of the values characteristic of the polymers of the invention- The high tensile strength of the novel polymers can be further increased by reinforcement with various fillers such as carbon black, various clays, calcium silicate, lignin or the like, .or the polymers may be softened by blending with appropriate plasticizers such as dioctyl phthalate or tricresyl phosphate. Alternatively the novel polymers themselves may be used as plasticizers for various resins such as polymers or copolymers of vinyl chloride or acrylonitrile, to give compounds of improved processability but of substantially shorter elongation than is possessed by polyvinyl chloride stocks blended with conventional high molecular weight plasticizers such as the rubbery butadiene-acrylonitrile copolymers or with high molecular weight polyesters. For example, blends of vinyl chloride resins with about 5 to 35% of the novel polymers have good extrusion rates at about 140 C. and the resulting blends which are characterized by a short ultimate elongation are useful for the manufacture of unbreakable phonograph records and the like.

The solubility of vulcanized stocks containing 20% and 40% combined butadiene respectively were evaluated in a number of solvents. The solubility experiments were carried out with stocks which had been compounded in accordance withthe recipe of Example 2 and which had been cured for minutes at 141 C. The solubility of the two cured stocks were the same and were as shown in the following table:

These data show that insolubilization had been effected by curing the polymers. The cured stocks were, of course, insoluble in all the solvents that did not attack the original, uncured polymer as described in Example 1 above.

The raw polymers showed little tendency toward resinification after 20 days air oven aging at 60 C. Also, the polymers showed negligible 6 discoloration after 200 hours Fadometer exposure or 20 days roof exposure.

EXAMPLE 4 Useful polymers of excellent tensile strength can also be prepared by copolymerizing a major proportion of dimethyl itaccnate with minor amounts of butadiene and a third monomer such as styrene. Three-component polymers were obtained applying the polymerization procedure of Example 1 to polymerizable feeds having the composition indicated in the subjoined table. The products have been found to have the following properties:

Run No O D Feed and Polymer Composition (Parts):

Butadiene 21 19 Dirnethyl itaccnate 63 55 Styrene 16 26 Raw Stock (Sheets pressed out at 141 C. for 15 minutes):

Tensile 670 570 Percent Elongation 1,930 620 Cured Stock (Cured at 141 C. with 1% Tuads and 1.5% Sulfur; no loading or plastioizer):

8 min. Tensile 870 2, 180 Percent Elongation 310 230 15 min. Tensile 1, 900 2, 400 Percent Elongation. 290 200 30 min. Tensile 2, 2, 510 Percent Elongation 260 150 The data indicate that the polymers are very fast curing and that they have good strength in both cured and uncured states. Increased styrene content can be seen to stiffen the product by increasing its tensile strength and decreasing its elongation.

The dimethyl i-ta'conate copolymers of this invention also offer a new source for the prepara-- tion of colloids of high molecular weight which form true solutions in water. Whereas the preparation of such water soluble polymers by direct polymerization is practically impossible, it has now been discovered that the copolymers of this invention can be saponified with alkali whereby the copolymers are converted into methyl alcohol and the corresponding water soluble alkali metal salt of the copolymer.

As long as the cop-olymer contains at least 65 weight percent of the vinyl ester by weight, the saponification can be accomplished by merely heating the polymer in the presence of 0.5 to 1.5 mol equivalents of aqueous alkali based on the combined este content of the polymer at a temperature between about 50 and C., i. e. at a temperature high enough for removal of the alcohol which forms the itaconic acid ester. Where water soluble derivatives are desired, about 0.9 to 1.2 mol equivalents of alkali should be used so as to effect substantially complete saponification. In certain cases it may be advisable to add small amounts of solvents, e. g. 1 to 10 parts of benzene or toluene based on the weight of dry polymer before the alkali treatment in order to swell the polymer and facilitate the saponification process. Such reagents as potassium, sodium or ammonium hydroxide or basic amines such as morpholine, alkyl amines and the like may be used as saponifi-cation agents. The saponification process may be carried out While the polymer is in latex form although such problems as foaming, polymer recovery and soap removal make this procedure somewhat less desirable than that involving the dry, washed polymer.

The water soluble polymers may be used for a number of applications such as paper impregnation, sizing and stiffenin or they may be used as detergents, as latex thickeners or as creaming agents. Then, too, the polyvalent metal derivatives may be prepared which may be of interest as lube oil and grease additives.

Examples illustrating the preparation of these soluble metal derivatives of the novel polymers are given below.

EXAMPLE 6 125 grams of a dry polymer obtained as described in Example 1 above was placed in a reaction flask with 1040 mls. of 1.0353 N potassium hydroxide solution, this being the stoichiometric amount of caustic required for complete saponification of the ester groups contained in the polymer. After heating the mixture with agitation for 6 hours at 75 0., a clear slightly viscous solution was obtained. This solution had the appearance and behavior of an ordinary sodium stearate soap solution and partial precipitation of polymer therefrom could be obtained by addition of a strong acid such as hydrochloric acid. When dried the aqueous solution of saponified polymer gave a soft sticky product which corresponded to the sodium salt of a copolymer of butadiene and itaconic acid. In contrast the neutralized precipitated polymer which corresponded to a copolymer of butadiene and itaconic acid was a hard brittle resin.

When an aqueous solution of the saponified polymer, 1. e. the potassium salt, was treated with solutions of various polyvalent metal salts such as zinc chloride, magnesium chloride, aluminum sulfate, barium chloride orcalcium chloride, waxy precipitates were thrown out of solution which were the corresponding polyvalent metal salts of the saponified polymers. These polymeric polyvalent metal salts, especially when derived from itaconate-butadiene copolymers which had been only partially-saponified so that, for example, about 50 to 80% of the ester groups originally present in the polymer are left unaffected, can be prepared in a form soluble in mineral oil or in greases and may be used as Valuable additives in conjunction therewith.

EXAMPLE 7 A copolymer of 100% conversion containing 15 I parts of butadiene and 85 parts of dimethyl itaconate was prepared as described in Example 2A and saponified as described in Example 6, except that the amount of potassium hydroxide used was increased to correspond stoi-chiometrically with the higher ester content of this polymer. When small portions, e. g. 0.05 to 2 percent of the saponified polymer or a water solution thereof were added to various latices, e. g. a Hevea rubber latex, a synthetic latex of GR-S or GR-A rubber or to latices of vinyl chloride polymers, a very pronounced thickening of the several latices was accomplished, and thereby the spreading and dipping characteristics of the latices were improved.

By contrast, attempts to saponify a copolymer containing 40 parts of dimethyl itaconate and 60 parts of butadiene, prepared and isolated substantially as described in Example 1, were unsuccessful. This polymer could not be converted into a water soluble product by saponification although the reaction mixture containing the polymer and 2 mols of alkali per mol of dimethyl itaconate combined in the polymer was heated for 24 hours at 80 to 90 C.

In another run a copolymer containing 60 parts of dimethyl itaconate and 40 parts of styrene was prepared and isolated substantially as described in Example 1. This polymer also could not be saponified sufficiently to form a water soluble product even after the polymer alkali mixture was heated for 24 hours at 80 to 90 C. Thus, it has been shown that not only the proportion of combined ester is critical for the purposes of this aspect of the invention, but, most surprisingly, the chemical nature of the monomer with which the itaconic ester has been copolymerized is critical as far as the saponification characteristics of the resulting copolymers are concerned. While certain preferred embodiments of the invention have been described above, it will be apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

The invention claimed is as follows:

1. A tough, thermoplastic copolymer of '75 to 80 parts of dimethyl itaconate and 25 to 20 parts of butadiene-1,3, characterized by a raw tensile strength of 750 to 900 lbs. per square inch and an ultimate elongation between 150 and 250%.

2. A tough, thermoplastic copolymer of 50 to 70 percent of dimethyl itaconate, 15 to percent of styrene and 10 to percent of butadiene- 1,3.

3. A method for preparing thermoplastic, resinous copolymers which comprises emulsifying a monomer mixture of 65 to 90 parts of dimethyl itaconate and 35 to 10 parts of butadiene-1,3 in water in the presence of 0.5 to 8 parts of an emulsifying agent and polymerizing the emulsified monomers in the presence of 0.3 to 0.5 part of an alkali metal persulfate catalyst and 0.1 to 1.0 part of a C6 to C18 alkyl mercaptan at a temperature between 30 and C.

4. A coating composition comprising 100 parts of methylethyl ketone, 10 to 25 parts of a resinous polymer composed of to 90 percent of combined dimethyl itaconate and 35 to 10 percent of combined butadiene-1,3, 2 to 10 parts of a polyhydric C2 to C3 alcohol and a trace of an acid catalyst.

5. A coating composition comprising'lOO parts of methylethyl ketone, 10 to 25 parts of a resinous polymer composed of 65 to 90 percent of combined dimethyl itaconate and 35 to 10 percent of combined butadiene-1,3, 2 to 10 parts of ethylene glycol and 0.01 to 1 part of toluene sulfonic acid.

6. A vulcanized composition comprising a copolymer of to parts of dimethyl itaconate and 25 to 20 parts of butadiene-1,3, and 0.5 to 3 parts of sulfur, said composition being characterized by a tensile strength of at least 1500 lbs. per square inch and an ultimate elongation below 350%.

7. A tough, thermoplastic, resinous copolymer of 65 to parts of dimethyl itaconate, and 35 to 10 parts of a conjugated C4 to C6 diolefin.

8. A vulcanized copolymer of 65 to 90 parts of dimethyl itaconate, and 35 to 10 parts of butadiene-l,3.

9. A tough, thermoplastic copolymer comprising a major proportion of dimethyl itaconate, and from 10 to 35% by weight of butadiene.

10. A vulcanized copolymer comprising a major proportion of dimethyl itaconate, and from 10 to 35% by weight of butadiene.

'11. A method for preparing thermoplastic, resinous copolymers which comprises emulsifying a monomer mixture comprising a major p tion of dimethyl itaconate, and from 10 to 35% by weight of butadiene in water in the presence of 0.5 to 8 parts of an emulsifying agent and polymerizing the emulsified monomers in the presence of 0.3 to 0.5 part of an alkali metal persulfate catalyst and 0.1 to 1.0 part of a C6 to C18 alkyl mercaptan at a temperature between 30 and 50 C.

12. A method for preparing thermoplastic, resinous ccpolymers which comprises emulsifying a monomer mixture of 50 to 70% of dimethyl itaconate, to of styrene, and 10 to of butadiene-1,3 in water in the presence of 0.5 to 8 parts of an emulsifying agent and polymerizing the emulsified monomers in the presence of 0.3 to 0.5 part of an alkali metal persulfate catalyst and 0.1 to 1.0 part of a C6 to C18 alkyl mercaptan at a temperature between 30 and C.

13. A method for preparing thermoplastic, resinous copolymers which comprises emulsifying REFERENQES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,294,226 DAlelio Aug. 25, 1942 2,384,569 Semon Sept. 11, 1945 2,427,063 Mighton et al Sept. 9, 1947 

1. A TOUGH THERMOPLASTIC COPOLYMER OF 75 TO 80 PARTS OF DIMETHYL ITACONATE AND 25 TO 20 PARTS OF BUTADIENE-1,3, CHARACTERIZED BY A RAW TENSILE STRENGTH OF 750 TO 900 LBS. PER SQUARE INCH AND AN ULTIMATE ELONGATION BETWEEN 150 AND 250%. 